1. Field of the Invention
The present invention relates generally to an image forming device having a fuser module and particularly to a fuser module that reduces force variability and positional variability within the fuser module.
2. Description of the Related Art
In an electro photographic image forming device such as a laser printer, an image forming unit transfers a toner image to a media sheet. After the toner image is transferred to the media sheet, the media sheet moves to a fuser module that applies heat and pressure on the media sheet in order to fuse the toner image to the media sheet.
The fuser module generally includes a backup roll, a fuser belt, and at least one heater. The backup roll and the fuser belt form a nip that is heated by the heater. When the media sheet enters the nip, it is gripped between the roller and the belt and is driven along the media path as the back-up roll and the fuser belt rotate, thereby fusing the toner image to the media sheet by the application of heat and pressure and eventually directing the media sheet out of the imaging apparatus. Typically, an entry guide is disposed upstream from the nip to guide the media sheet towards the nip.
An example of a conventional fuser module 10 is illustrated in FIG. 1. The fuser module 10 is placed between a first side frame 12 and a second side frame (not shown). The fuser module 10 includes a backup roll 14, a fuser belt 16, and a nip 18 formed by the backup roll 14 and the fuser belt 16. One end of the fuser belt 16 is covered by an end cap 20. The end cap 20 is mounted in a slot 22 formed in the side frame 12 of the image forming device and is held against the side frame 12 by a spring 24. The end cap 20 slides within the slot 22 based upon variation of the position of the nip 18 (shown by an arrow). A stationary entry guide 26 located upstream from the nip 18 is attached to the side frame 12 independent of the end cap 20 and guides the media sheet towards the nip 18 for fusing the toner image to the media sheet.
The position of the nip 18 often varies (shown by the arrow) due to several factors, such as wearing of the backup roll 14, thermal expansion of the backup roll 14, and variation in the media sheet thickness. However, a fuser module with the above geometry is unable to adjust itself in response to the above variations, thereby resulting in print defects.
For example, when the nip location varies (as shown by the arrow) due to the above reasons, the end cap 20 slides within the slot 22, thereby compressing or decompressing the spring 24 to accommodate for the nip location variation. Due to the compression and decompression of the spring 24, a large frictional force is developed between the end cap 20 and the side frame 12 of the image forming device around the slot 22. Also, the frictional force that is generated around the slot 22 directly affects the pressure that is maintained at the nip 18 in part due to a 1:1 aspect ratio (ratio of width to height) of the end cap 20. In other words, a considerable amount of the generated frictional force is deducted from the pressure that is maintained at the nip 18 and leads to application of decreased pressure on the media sheet passing through the nip 18. This relatively large force variation at the nip 18 causes inadequate fusing of the toner image to the media sheet resulting in compromised print quality.
Further, the stationary entry guide 26 that is fixed to the side frame 12 is independent of the movement of the nip 18, as well as the end cap 20. Also, a tip 28 of the entry guide 26 is placed at a certain distance from the nip 18. Thus, as the nip location varies due to the above reasons, the stationary entry guide 26 fails to adjust itself accordingly and the gap between the tip 28 of the entry guide 26 and the nip 18 increases, resulting in decreased media control. Consequently, this results in positional variation in the fuser module.
The introduction of the above-mentioned positional and force variability in the fuser module causes print defects, paper jams, belt skew, treeing, and smudging of the image on a media sheet passing through the nip. Thus, there is a need for a fuser module that addresses at least some of the above problems.